1. Field of the Invention
The present invention relates to a device having a multi-layered conductor structure including a transparent conductor layer comprising indium tin oxide (ITO), such as a liquid crystal display device, a charge coupled device (CCD), or a photoconductor stacked solid imaging device (PSID).
2. Description of the Related Art
A multi-layered conductor structure device, such as liquid crystal display device, CCD or PSID, is known which has, on a substrate, a first conductor layer which provides an electrode or wiring, an insulating film covering the first conductor layer and the substrate, and a second conductor layer formed on the insulating film and comprising ITO, which provides an electrode or wiring. For such a device, it is required that the first conductor layer have a low resistivity, and also have a high resistance to an etching liquid (a mixed liquid of nitric acid and hydrochloric acid) used for patterning the second ITO conductor layer.
Taking a liquid crystal display device as an example, an attention is greatly attracted to an active matrix type liquid crystal device provided with a thin film transistor (TFT) using an amorphous silicon (a-Si) film, as a switching element. It will be able to realize a large-area, highly fine, and high image quality panel display (a flat television) by constituting a TFT array using an a-Si film which can be produced at a low temperature on an inexpensive amorphous glass substrate.
In order for the active matrix type liquid crystal display device to display highly fine image, and have a large area, and an increased opening ratio of a pixel, it is necessary to make thin and long the signal lines to TFT, i.e., gate electrode wiring (gate line), or data wiring (data line). Further, in order to remove waveform distortion of the pulsed signals, it is necessary to sufficiently lower the resistivity of the wirings. Thus, the wiring materials must have a sufficiently small resistivity. For example, when a reverse stagger type TFT structure wherein a gate line is formed on a glass substrate, on which a TFT is formed by stacking an insulating film and a-Si film, is used, it is required that the gate line have a thin thickness and a sufficiently small resistivity, and can withstand chemical treatments performed during subsequent processes.
More specifically, a liquid crystal display device generally has an ITO electrode as a pixel electrode. In patterning the ITO electrode, an etching liquid for ITO (a mixed liquid of hydrochloric acid and nitric acid) contacts the gate line or the like through pinholes in the insulating film below the ITO. In such a case, the gate line material is corroded by the ITO-etching liquid, leading to the breakage of the gate line, unless the gate line material has a sufficient resistance to the ITO etching liquid.
As a gate line material which satisfies the above requirements to some extent, a metal film such as tantalum or titanium, or an alloy thereof (e.g., an Mo-Ta alloy disclosed in Published Examined Japanese Patent Application (kokoku) 61-48910) has been used. However, in order to realize a large-area, highly fine display device, a material is required which has a smaller resistivity, a good processability, and high resistance to chemicals during chemical treatments, particularly ITO patterning.
As a lower-resistivity material, a metal such as gold, aluminum, copper or platinum is being considered. However, if a storage capacitor line (Cs line) is formed of aluminum or copper, the Cs line would be broken during the subsequent process, since these metals have a poor resistance to etching liquids used to etch ITO, aluminum, silicon oxide, and silicon nitride. Further, gold, copper and platinum has a poor adhesivity with a substrate, often peeling off the substrate.
In the case of stagger type TFT structure wherein source and drain electrode wirings are formed on a substrate surface, the above properties or requirements are required for the source and drain electrode materials. In addition, the similar problems exist on liquid crystal display devices in general, and more generally on a device having a multi-layered conductor structure (including CCD and PSID) in which a conductor layer of ITO and various electrodes or wiring layers are laminated on each other through an insulating film.